Danielle Crittenden did exactly that:

It felt like someone had thrown a lit match in there. I began hopping around and breathing in the rapid, short puffs I'd learned in birth classes, so long ago, before I realized I didn't need to breathe like that if I took the epidural. I could really use a frikkin epidural right now.

Her takeway:

[I]f there is any smidgen of effect, it's notional, and probably only psychological. Overall, vodka-in-a-tampon seems a very inefficient, not to mention unpleasant, way to get drunk. I suppose the positive is that there is no danger of a second round. And I can't even imagine trying to do this at a party. You'd be walking around all night looking like you'd wet your pants, with a pleading expression on your face that said: Does anyone have a fire hose? In fact, maybe this is the way to kill this urban legend once and for all: Parents, I encourage you to urge your teenage girls to experiment with vodka tampons.

But not ecstasy pills up your butthole. Or maybe I shouldn't have written that.